Location Allocation (minimize facilities) providing strange results

justinhampton

I am trying to identify the minimum number of stations using the Location-Allocation minimize stations function.  I have 710 potential locations and roughly 40,000 demand points.  Based on the street speed limits, and the size of the area, I believe that all of the demand points could be reached by 7-9 stations within 4 minutes, and 4-5 stations in 8 minutes (just
eyeballing it based on previous service area maps). 

However, when I run the minimize facilities problem type using a 4 minute impedance in the location allocation tool, the results show approximately 21 stations, and many are within a thousand feet of each other.  There are only two settings: the impedance cut-off  (I'm using 4) and the impedance transformation (I'm using linear), am I doing this incorrectly? 

Any advice would be much appreciated, I've been working on this for a couple of days with much aggravation.

DougSterling

I am trying to identify the minimum number of stations using the Location-Allocation minimize stations function.  I have 710 potential locations and roughly 40,000 demand points.  Based on the street speed limits, and the size of the area, I believe that all of the demand points could be reached by 7-9 stations within 4 minutes, and 4-5 stations in 8 minutes (just
eyeballing it based on previous service area maps). 

However, when I run the minimize facilities problem type using a 4 minute impedance in the location allocation tool, the results show approximately 21 stations, and many are within a thousand feet of each other.  There are only two settings: the impedance cut-off  (I'm using 4) and the impedance transformation (I'm using linear), am I doing this incorrectly? 

Any advice would be much appreciated, I've been working on this for a couple of days with much aggravation.

You may have a disconnected network meaning that edges are not connected even though they look connected when you draw the network.  Can you route between the chosen facilities that are next to each other?

You may have a combination of restrictions that result in a disconnected network.  Try resolving without any restrictions.

If you are using hierarchy then you may have incorrect hierarchy values.  Try solving without hierarchy.

Your impedance cutoff of 4 may not be what you are expecting.  The impedance cutoff has the same units as the impedance attribute.  Make sure a value of 4 makes sense in light of your impedance attribute (which I assume is in minutes).

You may have accidentally added your stations to your network dataset as a junction source and your points are locating on them but they are disconnected from all edges in the graph.  Make sure that when you are locating your stations that you are locating only on your edges, not junctions.

Hope this helps.  The location-allocation solver should work in the way that you expect.

Doug